1. Field of the Invention
This invention relates to a method and apparatus for reducing the risk of rotational failure of orthopedic endoprostheses such as femoral prostheses. An apparatus has been designed and a method using this apparatus has been developed to enable making one or more grooves in the medullary canal surface of bones. The risk of rotational failure of the endoprostheses is reduced by implanting endoprostheses that interact with the grooves thereby securing the endoprosthesis in a desired position.
2. Description of Related Art
Each year a great many patients are relieved of severely debilitating injuries by surgical procedures to replace damaged joints. Of the more common of these operations are partial or total hip replacements. Patients suffering from rheumatoid or degenerative arthritis often derive great benefit from these surgical procedures. Additionally, femoral head necrosis requiring replacement with femoral head prostheses can result following fractures of the femur and has been associated with prolonged corticosteroid therapy.
Failure of implanted joint prostheses, however, is a complication often encountered that causes great pain and many times results in having to subject the patient to the risks and trauma of a surgical procedure to replace the failed prostheses. Many endoprostheses fail as a result of excessive loading of interfaces between the endoprosthesis and surrounding bone. As an example, femoral endoprostheses are constructed of a ball portion that extends above the proximal end of the femur and, attached to the ball, a shaft that is inserted into the medullary canal of the femur. Because of the smooth, relatively circular inner surface of the medullary canal of the femur, adequate mechanical stabilization of the endoprosthesis commonly is not attainable within that canal using current surgical methods. Rotation occurs because the materials and methods employed to secure the prosthetic shaft to the femur are unable to withstand the forces exerted upon the hip joint during movement.
To alleviate the pain and risks of further surgery associated with failure of femoral endoprostheses, efforts long have been directed to designing prostheses less likely to rotate and methods for securing these prostheses that produce bonds to the bone that are better able to withstand the torsional forces exerted upon the prostheses. U.S. Pat. No. 4,430,761 discloses a femoral head prosthesis constructed of a shaft provided with numerous parallel grooves which improve mechanical interaction with the cement placed in the bone cavity to bond the shaft to the bone.
U.S. Pat. No. 3,782,373, describes a jig that includes a shaft similar to the shaft of a femoral head prosthesis which jig is used as a guide for drilling holes in the femur to enable proper placement of screws that pass through the bone and engage the shaft of the prosthesis thereby securing it in the desired position.
As disclosed in U.S. Pat. No. 4,012,796, another approach to preventing failure of femoral head prostheses is to place an elastic collar in the proximal end of the femur which collar fits tightly around the prosthetic shaft to secure it in the desired position. Also, this collar is said to reduce the pressure exerted by the shaft of the prostheses on the femur thereby reducing the risk of necrosis which may cause prosthetic failure.
U.S. Pat. No. 4,284,080 discloses a cutting tool for shaping a femoral head to receive a shell-shaped prosthesis. This cutting tool is used to position prostheses that are attached to and supported by the femoral head rather than those that replace completely the previously removed femoral head. This cutting tool includes a blade for forming a cylindrical bore in the center of the femur to position the cutting tool as it shapes the femoral head to receive the prosthesis. To direct the blade that forms the cylindrical bore in the femur, the blade includes a guiding bore that fits over and, as the blade cuts the cylindrical bore, follows a guiding pin previously positioned in the center of the femur.
None of the references cited above and nothing in the prior art known to the present inventors teaches or suggests an apparatus or method for making one or more grooves in the medullary canal surface of a bone to provide surfaces that interact with and thereby reduce the risk of rotational failure of implanted prostheses.